Shock absorption material

ABSTRACT

A composite material with an elastic modulus of less than 0.1 MPa at 100% elongation including a polymer matrix and a non-Newtonian fluid is provided. The composite material may be employed in shock and impact absorption applications to reduce initial and shockwave acceleration forces. Methods of forming the composite material and reducing acceleration forces in an impact utilizing the composite material are also provided.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims priority to and the benefit of U.S. ProvisionalPatent Application No. 61/899,012, filed Nov. 1, 2013, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND

The present application relates generally to the field of materialshaving utility in products and applications that provide shockabsorption properties, such as those products and applications providingimpact protection. More particularly, the present application relates tomaterials that comprise a polymer matrix impregnated with anon-Newtonian (i.e., shear thickening) material.

Shock absorption materials have utility in a wide variety ofapplications in which it is desirable to damp or mitigate undesirableshocks to objects or to the human body (e.g., helmets, sports padding,exercise mats, bicycle and motorcycle seats, bumpers for movable cartsand other objects, and the like). Short term shocks (g-forces, measuredin N·kg, in contrast to impact forces, which are measured in N·m) may beinduced in impacts, drops, falls, earthquakes, and even explosions, andmay also occur during non-impact situations (e.g., during vehicleacceleration and deceleration, airplane descent and ascent, person beingpushed/pulled, etc.). By way of reference, impacts experienced by afootball lineman may regularly result in g-forces of betweenapproximately 20-30 g, and may in some instances produce forces inexcess of 100 g. Jogging may produce g-forces of between approximately 4and 6 g, while sprinting may produce g-forces of between approximately 8and 10 g. The g-forces generated by impacts and other sources of shockpose a direct threat to the well-being and survival of humans every day,and significant resources are devoted each year to finding new andbetter ways of providing shock resistance or mitigation. Additionally,the g-forces generated by impacts may produce long-term negative healtheffects, such as chronic traumatic encephalopathy (CTE).

Certain types of relatively hard and rigid forms of polyurethane andpolystyrene foams have been used in applications for shock absorption(e.g., in football helmets, etc.). These foams tend to be relativelydense. While such foams have the advantage of being able to withstandlarger impacts, one disadvantage of such foams is that they haverelatively limited compressibility, and may not optimally absorb theforces of smaller impacts experienced by the user and may not be ascomfortable as would be desirable for certain applications. Research hasshown that the cumulative effect of smaller, sub-concussive, impacts maybe long-term negative health effects that exceed those of a limitednumber of large concussive impacts. Pre-existing materials are notcapable of effectively absorbing both large impacts and small impacts,leaving a user susceptible to injury.

It would be advantageous to produce an improved material that mayprovide enhanced shock absorption and that reduces or eliminatesg-forces caused by impacts and other sources of shock. It would also beadvantageous to incorporate such a material into products so as toprovide enhanced shock protection. These and other advantages will beapparent to those reviewing the present disclosure.

SUMMARY

An exemplary embodiment relates to a composite material that comprises apolymer matrix (e.g., a foam material, although according to otherexemplary embodiments, other types of polymer matrix materials may beutilized) and a non-Newtonian fluid (sometimes referred to as a shearthickening material or dilatant) incorporated therein. The non-Newtonianfluid may be infused into a pre-prepared polymeric matrix material ormay be incorporated during the synthesis or polymerization of thepolymer matrix.

The composite material has an elastic modulus of less than 0.1 MPa at100% elongation, and includes a polymer matrix in the form of a foam anda non-Newtonian fluid impregnated in the polymer foam matrix. Thepolymer foam may be an open-cell foam or a closed-cell foam. The polymerfoam may have a density in the range of about 50 g/m³ to about 500,000g/m³. The polymer foam may be formed from a material selected from thegroup including elastomers, polystyrene, polyethylene, polypropylene,polyamide, polyurethane, ethylvinyl-acetate, polyethylene oxide,polyacrylate, cellulose, ethylene vinyl alcohol, polybutylene,polycaprolactone, polycarbonate, polyketone, polyester, polylactic acid,polyvinyl chloride, polyphenylene, and copolymers thereof. Thenon-Newtonian fluid may not be covalently bonded to the polymer foam.The non-Newtonian fluid may include at least one material selected fromthe group including polydimethylsiloxane, substitutedpolydimethylsiloxane, 1% w/v polyethylene glycol in water, 1% w/vpolyacrylamide in water, C8-silica particles in silicone oil, silicaparticles in glycerol, and tin oxide particles in water. Thenon-Newtonian fluid may have a viscosity in the range of about 60,000cSt to about 1,000,000 cSt. The non-Newtonian fluid may be hydrophobic.The composite material may have a density in the range of about 50 g/m³to about 5,000,000 g/m³. The non-Newtonian fluid may be present in anamount of about 10% to about 90% of the total weight of the compositematerial. The composite material may be incorporated into a productselected from the group including a helmet, clothing, a uniform,footwear, a glove, a case for an electronic device, a housing for anelectronic device, a vehicle seat, a vehicle headrest, a vehicledashboard, a vehicle door component, playground equipment, an exercisemat, a gym mat, and a packaging material. An initial impact accelerationforce and a shockwave acceleration force of an impact cushioned by thecomposite material may be less than an initial impact acceleration forceand a shockwave acceleration force of an equivalent impact cushioned bythe polymer foam alone. An impact cushioned by the composite materialmay produce initial impact acceleration forces that are at least about30% lower than an equivalent impact cushioned by the polymer foam alone.

Another exemplary embodiment relates to a product, apparatus, or device(collectively referred to as “products”) that incorporates a compositematerial such as that described in the preceding paragraph.Non-exclusive examples of products that may utilize such compositematerials include helmets (e.g., sports helmets for use in football,baseball, hockey, lacrosse, or other sports in which impacts may beexperienced, motorcycle and bicycle helmets, and any other type ofhelmet); padding for clothing or uniforms (e.g., shoulder pads, shinpads, knee pads, elbow pads, and any other type of padding worn by ahuman); footwear (shoe soles, etc.); gloves (e.g., work gloves, sportinggloves such as boxing gloves, hockey gloves, lacrosse gloves, etc.);cases or housings for electronics such as phones, computers, tablets,and the like; linings or padding for vehicle seats, child safety seats,and other types of seating; vehicle headrests, dashboards, doorcomponents, and other vehicle parts that may be impacted by a driver orpassenger in a vehicle collision; playground equipment lining; exerciseand gym mats; and packaging material for goods. Stated differently, thecomposite material may be incorporated into a helmet, clothing, auniform, footwear, a glove, a case for an electronic device, a housingfor an electronic device, a vehicle seat, a vehicle headrest, a vehicledashboard, a vehicle door component, playground equipment, an exercisemat, a gym mat, or a packaging material.

Another exemplary embodiment relates to a method of making the compositematerial and/or products made from or incorporating the compositematerial. For example, an exemplary method may include the steps ofproducing a non-Newtonian fluid, producing or forming a polymer matrix,and incorporating the non-Newtonian fluid into the polymer matrix. Inanother example, a method may utilize a non-Newtonian fluid in thesynthesis or polymerization of the polymer matrix such that thenon-Newtonian fluid is incorporated into the matrix immediately uponformation of the matrix. Still another example includes the steps ofproducing a composite material that comprises a polymer matrixincorporating a non-Newtonian fluid and incorporating the compositematerial into a finished product such as those described herein.

An exemplary method of forming the composite material includes mixing anon-Newtonian fluid and a first polymer foam matrix precursor to form amixture, adding a second polymer foam matrix precursor to the mixture ofthe non-Newtonian fluid and the first polymer foam matrix precursor,mixing the mixture of the non-Newtonian fluid, first polymer foam matrixprecursor, and second polymer foam matrix precursor to form a mixture;wherein mixing the mixture of the non-Newtonian fluid, first polymerfoam matrix precursor, and second polymer foam matrix precursor resultsin the foaming of the mixture and the formation of a polymer foam matrixmaterial, and curing the mixture of the non-Newtonian fluid, firstpolymer foam matrix precursor, and second polymer foam matrix precursorto form the composite material. The formed composite material has anelastic modulus of less than 0.1 MPa at 100% elongation. The method mayfurther include disposing the mixture of the non-Newtonian fluid, firstpolymer foam matrix precursor, and second foam polymer matrix precursorin a mold prior to curing the mixture.

A method of reducing acceleration forces in an impact may includedisposing a composite material between an impact object and an impactsurface. The composite material has an elastic modulus of less than 0.1MPa at 100% elongation and includes a polymer foam matrix and anon-Newtonian fluid impregnated in the polymer foam matrix. An initialimpact acceleration force and a shockwave acceleration force of theimpact may be less than an initial impact acceleration and a shockwaveacceleration of an equivalent impact with the polymer foam alonedisposed between the impact object and the impact surface. The impactmay produce an initial impact acceleration force that is at least about30% lower than an equivalent impact with the polymer foam alone disposedbetween the impact object and the impact surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are graphs illustrating comparative test results for droptests performed at 5, 7.5, and 11 inches, respectively.

FIG. 4 is a graph illustrating expected shock absorption profiles fornormal impacts as compared to cushioned impacts.

FIG. 5 is a pair of graphs comparing shock absorption profiles ofpolyurethane and polystyrene foams.

FIG. 6 is a pair of graphs comparing shock absorption profiles ofpolystyrene and polystyrene impregnated with water.

FIG. 7 is a pair of graphs comparing shock absorption profiles ofpolystyrene impregnated with two different non-Newtonian fluids.

FIGS. 8(a)-8(d) illustrate a series of graphs summarizing the shockabsorption behavior of polystyrene impregnated with select non-Newtonianfluids.

FIG. 9 provides a description of a polymerization process incorporatinga non-Newtonian fluid according to an exemplary embodiment.

FIG. 10 is a graph comparing the shock absorption performance ofpolyurethane form to that of PDMS-impregnated polyurethane foam.

FIGS. 11(a) and 11(b) are graphs comparing the shock absorption profilesof polyurethane foam by itself and PDMS-impregnated polyurethane foam,respectively.

FIG. 12 is a graph comparing the impact drop test results of anunmodified helmet and a helmet modified to utilize a polyurethanefoam-non-Newtonian fluid composite material.

FIGS. 13(a)-13(c) illustrate various perspective views of an impact droptest rig, according to an exemplary embodiment.

FIGS. 14(a)-14(c) depict graphs comparing the acceleration forces of animpact in a drop test of polyurethane foam, a polyurethane andnon-Newtonian fluid composite material with an elastic modulus ofgreater than 0.1 MPa at 100% elongation, and a polyurethane andnon-Newtonian fluid composite material with an elastic modulus of lessthan 0.1 MPa at 100% elongation, respectively.

DETAILED DESCRIPTION

According to an exemplary embodiment, a shock absorption materialincludes a polymer matrix (e.g., a polymer foam such as a polystyrene orpolyurethane foam, although other materials may be used according toother exemplary embodiments as described herein, including copolymers ofvarious types) impregnated with a non-Newtonian fluid to provideenhanced shock absorption characteristics for the material and productsincorporating such a material. A wide variety of non-Newtonian fluidsmay be utilized, either alone or in combination with each other,depending on the particular performance characteristics, manufacturingconsiderations, and other factors.

A non-Newtonian fluid is a fluid that is characterized by the fact thatits shear viscosity increases with applied shear stress. A non-Newtonianfluid may sometimes be referred to as a shear thickening material ordilatant, and for purposes of the present disclosure, the three termswill be used interchangeably. For example, a non-Newtonian fluid mayexhibit the properties of a liquid when the material is at rest, butwhen a force or stress is applied to the material, the material beginsto essentially “thicken” and adopt some properties of a solid material.One well-known example of a non-Newtonian fluid is a mixture ofcornstarch and water sometimes referred to as “oobleck,” which exhibitscertain shear-thickening characteristics when a stress is applied to thematerial.

According to an exemplary embodiment, the composite material may beformed of a relatively soft foam matrix (e.g., a polystyrene foam, apolyurethane foam, etc.) having a non-Newtonian fluid incorporatedtherein. A soft foam matrix may refer to a matrix material that ishighly compressible. One advantageous feature of such a compositematerial is that the material may act as a soft foam under normalconditions in which little or no forces/stresses are applied to thematerial, and when larger forces/stresses are applied, the materialincrease in stiffness and/or hardness to better absorb the shock orimpact. Because the softening/hardening effect is reversible, thecomposite material will return to its original soft-foam-like behavior,such that the material can be used for relatively long periods of timewhile retaining its shock-absorbing effectiveness in response to appliedforces/stresses. The composite material is capable of providing impactprotection over a larger range of forces than is typical of pre-existingfoam materials.

The polymeric matrix may be formed from any of a wide variety ofmaterials, including, for example, natural and synthetic elastomers(e.g., cis-polyisoprenes, trans-polyisoprenes, polybutadiene, neoprene,butyl rubber (both halogenated and unhalogenated), nitrile, siliconerubber, fluorosilicone rubber, and polyacrylonitrile), polystyrene,polyethylene (high density and low density), polypropylene, polyamide,polyurethane, ethylvinyl-acetate, polyethylene oxide, polyacrylate,cellulose, ethylene vinyl alcohol, polybutylene, polycaprolactone,polycarbonate, polyketone, polyester, polylactic acid, polyvinylchloride, and polyphenylene. According to other exemplary embodiments,the polymer matrix may include any combination of the polymers as acopolymer (including alternating, periodic, random, block and graftcopolymers). According to other exemplary embodiments, the polymermatrix may include fluorinated versions of any of the foregoing polymersor any of the foregoing polymers that have been substituted with otherbranched alkyl, aryl, or halogenated substitutions.

According to a particular exemplary embodiment, the polymer matrix isformed of a relatively soft polystyrene foam. In general, polystyrenetends to be less dense than polyurethane, which makes it more suitablefor absorbing the impact forces of small objects as compared topolyurethane, while the increased density of polyurethane allows it tobe more capable of absorbing forces of large impacts as compared topolystyrene (additionally, polyurethane may be better in certainapplications where water and sweat are present, since it is lesssusceptible to water vapor absorption and mold growth than polystyrene).Both polystyrene and polyurethane (and other polymers, such as thosedescribed above) may be formed into relatively soft foams, and theinventors have advantageously incorporated a non-Newtonian fluid intorelatively soft foams to provide enhanced shock absorption propertiesfor the foam. As will be described in more detail below, theincorporation of a non-Newtonian fluid into the polystyrene foam maydramatically alter the overall shock absorption capabilities of thematerial, making it far more suitable for use in shock absorptionapplications.

According to an exemplary embodiment, the polystyrene foam has a densityof between approximately 50 g/m³ and approximately 500,000 g/m³, such asbetween approximately 50,000 g/m³ and approximately 500,000 g/m³ and,according to a particular exemplary embodiment, approximately 100,000g/m³. Of course, other types of foam and other densities may be utilizedaccording to other exemplary embodiments.

According to other exemplary embodiments, the polymer matrix may beformed from any of the other materials described herein, and may havediffering materials properties that may be tailored or selected for aparticular application as desired.

The non-Newtonian fluid may be selected from any of a variety ofmaterials that exhibit shear thickening behavior, non-exclusive examplesof which include polydimethylsiloxanes, 1% w/v polyethylene glycol inwater, 1% w/v polyacrylamide in water, or polydimethylsiloxanes withother alkyl, alkenyl, alkynyl, phenyl, or halogenated substitutions inplace of the methyl group. Other possibilities include C8-silicaparticles in a silicone oil, silica particles in glycerol, and tin oxideparticles in water. According to one embodiment, the non-Newtonian fluidis not covalently bonded to the polymer foam matrix. Covalent bondsbetween the polymer foam matrix and the non-Newtonian fluid mayconstrain the movement of the non-Newtonian fluid in response to animpact, preventing the effective absorption of impact energy and theeffective reduction of impact energy acceleration forces. Covalent bondsbetween the polymer foam matrix and the non-Newtonian fluid may alsoundesirably change the properties of the polymer foam, such as byincreasing the density of the polymer foam.

According to an exemplary embodiment, the non-Newtonian fluid may have aviscosity in the range of between approximately 60,000 cSt andapproximately 1,000,000 cSt. According to other exemplary embodiments,the non-Newtonian fluid may have a viscosity of between approximately100,000 cSt and approximately 500,000 cSt.

According to an exemplary embodiment, the composite material (i.e., thefoam having the non-Newtonian fluid incorporated therein) may have adensity in the range of between approximately 50 g/m³ and approximately5,000,000 g/m³, such as between approximately 50 g/m³ and approximately3,000 g/m³ or between approximately 15,000 g/m³ and approximately400,000 g/m³. According to other exemplary embodiments, the compositemay have a density of between approximately 5,000 g/m³ and approximately5,000,000 g/m³, while in still other exemplary embodiments, the densitymay be between approximately 50,000 g/m³ and approximately 500,000 g/m³.According to a particular exemplary embodiment, the composite may have adensity of approximately 100,000 g/m³. The density of the compositematerial may be directly correlated to the elastic modulus of thecomposite material, such that lower density composite materials may havelower elastic moduli. Low density composite materials may also reducethe weight of products including the composite materials.

The composite material may have an elastic modulus at 100% elongation ofless than approximately 0.1 MPa. According to a particular exemplaryembodiment, the composite material may have an elastic modulus at 100%elongation of between approximately 0.001 MPa and approximately 0.1 MPa,such as between approximately 0.01 MPa and approximately 0.05 MPa. Theelastic modulus indicates the elastic behavior of the compositematerial. A low elastic modulus indicates a highly compressiblematerial, and highly compressible materials are well suited to reducingimpact acceleration forces in small impact events. Additionally,composite materials with elastic moduli below approximately 0.1 MPa arecapable of reducing the shockwave acceleration forces in an impactevent. Shockwave acceleration forces are the acceleration forcesproduced as a result of an impact after the initial impact accelerationforces, as shown in FIG. 4.

According to an exemplary embodiment, the non-Newtonian fluid may beprovided at a level of between approximately 10 percent andapproximately 90 percent of the total weight of the composite material.According to a particular exemplary embodiment, the non-Newtonian fluidmay be approximately 30 percent of the weight of the composite material.According to other exemplary embodiments, the weight percentage of thenon-Newtonian fluid in the composite material may be varied depending onthe particular performance criteria desired and other factors.

Any of a variety of methods may be used to incorporate the non-Newtonianfluid into the polymeric matrix. For example, according to an exemplaryembodiment, the composite could be made by incorporating thenon-Newtonian fluid before the polymerization/foaming process ofelastomer by adding the non-Newtonian fluid to one of the precursormaterials used to form the polymer matrix. According to anotherexemplary embodiment, the composite can be made by adding thenon-Newtonian fluid to a polymerized/foamed elastomer using injection orabsorption methods. According to one embodiment, the non-Newtonian fluidis uniformly or homogenously dispersed in the polymer foam matrix.

Experimental testing was performed to determine the efficacy ofincorporating non-Newtonian fluids into polymer matrices for enhancingthe shock absorption properties thereof. Two non-Newtonian fluids wereused in the testing: (1) a polyacrylamide/water non-Newtonian fluidcharacterized as having a generally linear polymer chain, a molecularweight of greater than 1,000,000, and minimal hydrogen bonding, and (2)a polyethylene glycol/water non-Newtonian fluid characterized as havinga generally linear polymer chain, a molecular weight of greater than4,000,000, and a large degree of hydrogen bonding.

Five series of samples were produced to assess shock absorptionperformance: (1) polyurethane foam with no incorporated non-Newtonianfluid (PU), (2) polystyrene foam with no incorporated non-Newtonianfluid (PS), (3) polystyrene foam with water incorporated therein(PS-H₂O); (4) polystyrene foam with a polyacrylamide/water non-Newtonianfluid incorporated therein (PS-PA), and (5) polystyrene foam with apolyethylene glycol/water non-Newtonian fluid incorporated therein(PS-PEO). Additional information regarding the five samples is providedbelow in Table 1.

TABLE 1 Foam Foam Foam Composite Foam volume Weight Density MaterialMaterial Fluid (cm³) (g) (g/cm³) PU Polyurethane none 135 4 0.02962963PS Polystyrene none 135 4 0.02962963 PS-H₂O Polystyrene H₂O 135 340.251851852 PS-PA Polystyrene polyacrylamide/ 135 34 0.251851852 H₂OPS-PEO Polystyrene polyethylene 135 34 0.251851852 glycol/H₂O

To test the shock absorption performance of the materials, each of thesamples was placed on a flat surface and an impact object weighing 1.5pounds that was fitted with an accelerometer was dropped onto each ofthe samples from three different heights. FIGS. 1-3 graphicallyillustrate the g-forces experienced by the samples when objects weredropped from heights of 5 inches, 7.5 inches, and 11 inches,respectively. Multiple drops were performed for each sample, and thenumbers illustrated graphically represent the average results from themultiple tests. As illustrated in FIG. 1, all of the polystyrene-basedmaterials appear to better absorb g-forces at a relatively low dropheight as compared to polyurethane foam, this may be a function ofhigher compressibility of the polystyrene-based materials. Eachcomposite material exhibited a reduction in g-forces of greater thanabout 60% in comparison to the polyurethane foam. Additionally, itappears that each composite material (i.e., polystyrene impregnated withwater or a non-Newtonian fluid) outperforms polystyrene foam by itself.From this data, it appears that the addition of both water and anon-Newtonian fluid may improve the shock absorption performance of thepolystyrene foam.

FIG. 2 graphically illustrates the shock absorption performance of thepolystyrene foam and polystyrene foam composites when dropped from aheight of 7.5 inches. In this case, it appears that thewater-impregnated polystyrene is marginally better at absorbing g-forcesthan polystyrene by itself (nearly an 8% reduction), while the additionof non-Newtonian fluids into the polystyrene foam both decrease theamount of g-forces experienced by more than 15%, suggesting asignificant improvement through the addition of non-Newtonian fluidsinto the polymer matrix.

FIG. 3 graphically illustrates the shock absorption performance of thepolystyrene foam and polystyrene foam composites when dropped from aheight of 11 inches. At this height, a difference between the twodifferent non-Newtonian fluids became apparent, with thepolyacrylamide-impregnated polystyrene foam showing similar performanceas the water-impregnated polystyrene foam (suggesting that thepolyacrylamide-impregnated foam has exceeded its damping capability atthis height), while the polyethylene glycol impregnated polystyrene foamsignificantly outperformed the other foams. One possible explanation forthe differing performance of the two different non-Newtonian fluids maybe the difference in the extent of the hydrogen bonding between the twomaterials, with the polyethylene glycol having significantly morehydrogen bonding as compared to the polyacrylamide.

Next, the shock absorption profiles of the different materials weremeasured to understand the differences between them. FIG. 4 illustratesshock absorption profiles for typical and cushioned impacts, while FIGS.5-7 illustrate the shock absorption profiles for the various materialsdiscussed above. FIG. 5 illustrates that polystyrene foam absorbs impactover a longer period of time in comparison to polyurethane, asdemonstrated by the broader peaks observed for the polystyrene material.This data indicates that the polystyrene material appears to be morecompressible than the polyurethane material. Each of the impregnatedpolystyrene foams have a different shock profile than thenon-impregnated polyurethane and polystyrene foams, with the secondaryshockwave after initial impact being significantly diminished in theimpregnated foams as compared to the non-impregnated foams. FIG. 8summarizes the initial results. The polyethylene glycol impregnatedpolystyrene foam demonstrates a moderate decrease in g-forcesexperienced compared to water-impregnated polystyrene andnon-impregnated polystyrene (˜13% reduction) and greatly attenuates theg-forces experienced compared to polyurethane foam (>70% reduction), asshown in FIGS. 8(a) and 8(b), respectively. The material also adopts ashock absorption profile as shown in FIG. 8(d) that is consistent withabsorption of g-force over increased time as well as a greatlydiminished shockwave after initial impact in comparison to the shockabsorption profile of the polyurethane foam as shown in FIG. 8(c).

Notably, after each drop, it was apparent that the foams impregnatedwith non-Newtonian fluid returned to their pre-drop states having arelatively soft foam-like-behavior. This suggests that the enhanceddampening and shock absorption of the impregnated foams was the resultof a temporary shear thickening of the non-Newtonian fluid, whichreversibly transitioned back to its pre-stress state in repeatablefashion. As a result, it would be expected that in normal use (i.e.,before shock is applied to the material) the foams would have arelatively soft and cushioned feel, and that the application of shockwill case a temporary and reversible hardening of the material to absorbthe shock, after which the foam will return to its original state.Advantageously, this may provide a soft and cushioned feel for a user incertain applications (e.g., helmets, gloves, etc.) to provide improveduser comfort during normal use. The composite material is thereforecapable of absorbing both small impacts when acting as a soft foam andlarge impacts upon hardening, providing protection against a largerrange of impacts than pre-existing foam materials which are directed toabsorbing either small impacts or large impacts.

Because non-Newtonian fluids such as polyacrylamide and polyethyleneglycol are water soluble, it is possible that their effectiveness atabsorbing shock in applications where water exposure is present may belimited. Under certain circumstances, evaporation and environmentaleffects may also play a role in diminishing the effectiveness of thenon-Newtonian fluid impregnated polymer matrices. Accordingly it may beadvantageous for certain applications to encase the composites in apolymer coating or “skin” to control environmental impact on theeffectiveness of the material.

According to another exemplary embodiment, the effect of the surroundingenvironment may be mitigated by utilizing a hydrophobic material inplace of a water-based non-Newtonian fluid and/or incorporating thenon-Newtonian fluid prior to polymerization of the polymer matrix in aneffort to “trap” the non-Newtonian fluid within the foam and combatevaporation and other environment-related concerns.

FIG. 9 provides an overview of a process for preparing a compositematerial that involves adding a non-Newtonian fluid (in this case, highmolecular weight polydimethylsiloxane, otherwise referred to as PDMS) tothe components used in synthesizing a polymer (polyurethane) foam (inthis case, a low molecular weight polyol (polyether chain) andmethylene-diphenyl-diisocyanate (MDI)). After the components are mixed,the polyol and MDI begin to polymerize, incorporating the PDMS duringthe polymerization process. Excess MDI releases CO₂, foaming thematerial. The PDMS is inert during the polymerization process, such thatthe PDMS is not covalently bonded to the polymer foam matrix. Theresulting polyurethane foam has a far lower density than thepolyurethane foam discussed in the context of FIGS. 1-8, and moreclosely resembles the feel and density of the polystyrene foamsdiscussed previously.

According to other exemplary embodiments, different non-Newtonian fluidsand foam precursors may be used, depending on the desired performancecharacteristics of the composite material, manufacturing considerations,and/or other factors. It bears noting that the PDMS was found to besoluble in the polyol, which was found to aid in the complete dispersionor homogenization of the non-Newtonian fluid throughout the resultingcomposite material. The polyol, MDI, and PDMS were then polymerizedtogether while the non-Newtonian fluid was in solution, which allowedfor the production of a composite material with a fully incorporated and“trapped” non-Newtonian fluid within the polymer foam matrix. Oneparticularly advantageous feature of using relatively long-chain PDMS isthat it does not evaporate during normal use, thereby providing enhancednon-Newtonian fluid properties and being water resistant.

FIGS. 10, 11(a) and 11(b) depict the shock absorption performance ofnon-impregnated and PDMS-impregnated low-density polyurethane foams, theshock absorption profile of non-impregnated low-density polyurethanefoam, and the shock absorption profile of PDMS-impregnated low-densitypolyurethane foam, respectively. Because the low-density polyurethanefoam has a higher density than the polystyrene foams described above,the weight of the object used in the 3.5 inch drop tests was increasedto 15 pounds. Additionally, the use of an object weighing 15 poundsbetter simulates the effects on impacts to human heads, as a typicalhigh school student's head weighs approximately 15 pounds.

The composite material exhibited a roughly 30% improvement in shockabsorption compared to the greater than 20 g acceleration experienced bythe non-impregnated foam. The shock absorption profile of the compositematerial also showed a higher degree of secondary shock wave reductionas compared to the non-impregnated material, thus providing furtherevidence of the improvement in shock absorption performance of thepolymer containing a non-Newtonian fluid. It is also expected that themanufacturing process used in the creation of the composite materialwill provide for more consistent shock reduction performance over a widerange of use conditions, since the incorporated non-Newtonian fluidwould be expected to be less susceptible to adverse impact from localenvironmental conditions (e.g., moisture, evaporation, etc.) because ofits incorporation during the polymerization process for the foam.Additionally, incorporation of the non-Newtonian fluid during thepolymerization process of the foam allows the non-Newtonian fluid to beincorporated in to closed-cell foams and the production of compositematerials in which the non-Newtonian fluid is uniformly andhomogeneously distributed in the polymer foam matrix. The use of aclosed-cell foam may allow the non-Newtonian fluid to be fullyencapsulated within the foam, preventing the leaching of thenon-Newtonian fluid from the composite material and rendering thecomposite material waterproof and unaffected by environmentalcontaminants, such as sweat.

According to a variety of exemplary embodiments, the composite materialsherein may be incorporated into a wide variety of products, apparatuses,or devices (collectively referred to as “products”). Non-exclusiveexamples of products that may utilize such composite materials includehelmets (e.g., sports helmets for use in football, baseball, hockey,lacrosse, or other sports in which impacts may be experienced,motorcycle and bicycle helmets, and any other type of helmet); paddingfor clothing or uniforms (e.g., shoulder pads, shin pads, knee pads,elbow pads, and any other type of padding worn by a human); footwear(shoe soles, etc.); gloves (e.g., work gloves, sporting gloves such asboxing gloves, hockey gloves, lacrosse gloves, etc.); cases or housingsfor electronics such as phones, computers, tablets, and the like;linings or padding for vehicle seats, child safety seats, and othertypes of seating; vehicle headrests, dashboards, door components, andother vehicle parts that may be impacted by a driver or passenger in avehicle collision; playground equipment lining; exercise and gym mats;and packaging material for goods.

Although the present disclosure contemplates a wide variety of compositematerials and methods of making the same, the following examples areprovided by way of illustration, and are not intended as limiting withrespect to the present disclosure and the scope of the inventionsdescribed herein. Accordingly, it should be understood that othermaterials and combinations of materials, and methods of making the same,are contemplated by the present disclosure and are intended to be a parthereof.

Example 1 Polyacrylamide/Polystyrene Composite Material

In a first example, a polyacrylamide/polystyrene composite material maybe produced according to the following procedure.

For the non-Newtonian fluid, 1.5 grams of polyacrylamide (molecularweight >1,000,000) is added to a mixing container, and 150 mL of wateris added to the container with the polyacrylamide. To aid in thedissolving of the polyacrylamide, the solution is slowly poured back andforth between two containers until the polyacrylamide is completelydissolved. Once the polyacrylamide is completely dissolved, the processof pouring the solution back and forth between the two containers iscontinued for between approximately 5 and 10 minutes, after which thesolution is allowed to rest for between approximately 1 and 2 hours. Toensure correct mixing, the solution is then checked to confirm that thesolution has the ability to self-siphon (Self-siphoning fluids tend tobe solutions of long chain polymers, and self-siphoning refers to theability of the solution to “pull” the solution over the crest of thecontainer without any added force; once the fluid goes past the crest ofthe container, the fluid that has made it over the crest will simplypull the rest of the solution out of the container with no additionalforce; this is sometimes referred to as a “tubeless siphon”). Theresulting non-Newtonian fluid is a 1% w/w solution of polyacrylamide inwater (e.g., 150 grams of non-Newtonian fluid solution would include 1.5grams of polyacrylamide and 148.5 grams of water).

To incorporate the non-Newtonian fluid into a polymer matrix, apreferred size of polystyrene foam (e.g., sized for a particular productor application) is cut or otherwise formed, and the desired amount ofnon-Newtonian fluid (in this case, polyacrylamide in water) is measuredout. The non-Newtonian fluid is then dispersed across the top of thefoam and is absorbed into the foam. According to an exemplaryembodiment, the absorption process may take approximately five minutes,although according to other exemplary embodiments, the amount of timefor absorption may differ depending on a variety of factors, includingthe amount of non-Newtonian fluid and size/shape of foam, the types ofnon-Newtonian fluid and foam used, and other factors). After theabsorption is complete, the foam is repeatedly compressed anddecompressed for a suitable amount of time to ensure that thenon-Newtonian fluid is uniformly dispersed throughout foam.

Example 2 Polyethylene Glycol/Polystyrene Composite Material

In a second example, a polyethylene glycol/polystyrene compositematerial may be produced according to the following procedure.

For the non-Newtonian fluid, 4 grams of polyethylene glycol (molecularweight of approximately 4,000,000) are added to a mixing container.Approximately 40 mL of ethanol, isopropanol, or acetone are then addedto the polyethylene glycol while stirring rapidly to ensure thataggregation does not occur. Stirring continues until the solution iscompletely homogenous (e.g., for approximately 10 minutes, although thetime may differ depending on the solvent selected). During the stirringprocess, 400 mL of water is slowly added to avoid aggregation within thesolution. The solution is then slowly poured back and forth between twocontainers until the solution is completely homogenous, after which thesolution may be checked to ensure that it self-siphons. The solution maythen be allowed to rest for a suitable time (e.g., approximately 4hours) to allow the alcohol to evaporate. The resulting non-Newtonianfluid is a 1% w/v solution of polyethylene glycol.

To incorporate the non-Newtonian fluid into a polymer matrix, apreferred size of polystyrene foam (e.g., sized for a particular productor application) is cut or otherwise formed, and the desired amount ofnon-Newtonian fluid (in this case, polyethylene glycol) is measured out.The non-Newtonian fluid is then dispersed across the top of the foam andis absorbed into the foam. According to an exemplary embodiment, theabsorption process may take approximately five minutes, althoughaccording to other exemplary embodiments, the amount of time forabsorption may differ depending on a variety of factors, including theamount of non-Newtonian fluid and size/shape of foam, the types ofnon-Newtonian fluid and foam used, and other factors). After theabsorption is complete, the foam is repeatedly compressed anddecompressed for a suitable amount of time to ensure that thenon-Newtonian fluid is uniformly dispersed throughout foam.

Example 3 Polydimethylsiloxane/Polyurethane Composite Material

In a third example, a polydimethylsiloxane/polyurethane compositematerial may be produced according to the following procedure.

An appropriate amount of non-Newtonian fluid (e.g.,polydimethylsiloxane) is measured out for a desired w/w percentage for agiven application. For example, a 30% w/w composite ofpolydimethylsiloxane in urethane would require 10 grams ofpolydimethylsiloxane for 32 grams composite (other 22 grams is thepolyurethane foam matrix). Once the polydimethylsiloxane is measuredout, the appropriate amount of monomer A (16.5 grams polyol) is weighedand added to the previously-measured polydimethylsiloxane. Thesecomponents are then mixed together until completely homogenous. Anisocyanate cross linker (11 grams) is added to thepolyol-polydimethylsiloxane solution mixture and mixed until homogenous.According to an exemplary embodiment, the mixing is completed in arelatively short time frame (e.g., approximately 30 seconds), at whichpoint the polymerization and foaming process begins to take place.According to an exemplary embodiment, the ratio of monomer A (polyol) tomonomer B (isocyanate) is 60:40. This can be adjusted appropriately forthe desired application; however, there must be excess isocyanatepresent (determined by molar equivalents of isocyanate to polyol) toproduce the CO₂ needed for foaming (otherwise an additional foamingagent will need to be introduced). The composite material is thenallowed to cure for approximately 24 hours at room temperature.According to other exemplary embodiments, the curing may be performed atapproximately 60 degrees Celsius, such as by disposing the foam in amold heated to a consistent temperature by an oven or water bath.According to still other exemplary embodiments, the curing time andtemperature may vary according to other exemplary embodiments dependingon the constituents used and other factors.

Example 4 Polydimethylsiloxane/Polyurethane Composite Material

In a fourth example, a polydimethylsiloxane/polyurethane compositematerial may be produced according to the following procedure.

A mixture was formed by adding 60 parts by weight of a polyol solutionand 35 parts by weight of polydimethylsiloxane (PDMS) 300,000 cSt to amixing container. The polyol and PDMS mixture was then mixed with adrill mixer attachment at greater than 1,000 revolutions per minute(RPM), producing a blended mixture that was white in appearance, frothy,and bubbly. An isocyanate solution in an amount of 40 parts by weightwas then added to the blended polyol and PDMS mixture, and theisocyanate/polyol/PDMS mixture was then mixed with a drill mixerattachment at greater than 1,000 RPM for approximately 15-20 secondsuntil the blended mixture started to foam. The foaming mixture was thenquickly transferred to an aluminum mold that was pre-treated with ananti-stick coating, and the top cover of the mold was secured over themold cavity and fastened with clamps. After curing for approximately4-24 hours, the PDMS/polyurethane composite material was removed fromthe mold.

Example 5 Silicone Foam Composite Material

In a fifth example, a silicone foam composite material may be producedaccording to the following procedure.

A mixture was formed by adding 40 parts by weight of a polyorganosilanesolution and 30 parts by weight of polydimethylsiloxane (PDMS) 300,000cSt to a mixing container. The polyorganosilane and PDMS mixture wasthen mixed with a drill mixer attachment at greater than 1,000revolutions per minute (RPM), producing a blended mixture that was whitein appearance, frothy, and bubbly. A siloxane catalyst solution in anamount of 80 parts by weight was then added to the blendedpolyorganosilane and PDMS mixture, and the mixture was then mixed with adrill mixer attachment at greater than 1,000 RPM for approximately 15-20seconds until the blended mixture started to foam. The foaming mixturewas then quickly transferred to an aluminum mold that was pre-treatedwith an anti-stick coating, and the top cover of the mold was securedover the mold cavity and fastened with clamps. After curing forapproximately 20 minutes, the silicone foam composite material wasremoved from the mold and allowed to cure for an additional 24 hours toallow the composite to achieve full strength.

Example 6 Helmet Impact Tests

Helmet impact tests were carried out utilizing an impact drop rig 100 ofthe type shown in FIGS. 13(a)-13(c). The helmet drop rig 100 wasanalogous to a NOCSAE twin wire, frictionless drop assembly, and wasoutfitted with a hybrid III dummy head neck/assembly 110. The hybrid IIIdummy head/neck assembly 110 was secured to the base of the dropcarriage 120 such that the head/neck assembly would contact an impacttarget 130 during an impact drop test, and the head neck assembly 110was outfitted with an accelerometer located at the center of gravity ofthe dummy head. The accelerometer was configured to measure theacceleration forces produced during a helmet drop test in when thehead/neck assembly 110 contacts the impact target 130.

A Riddell Speed Classic Helmet was then modified by stripping the foamprovided by the manufacturer and replaced with the polyurethane foamcomposite material produced in Example 4. The polyurethane foamcomposite material utilized in the modified helmet had the same shapeand thickness as the manufacturer supplied foam. For the sake ofcomparison, an unmodified helmet was subjected to impact drop tests inparallel with the modified helmet. Drop heights of 6, 12, 24, 36, and 48inches were employed utilizing the helmet drop rig 100 with the helmetmount on the dummy head/neck assembly 110, and peak acceleration forceswere measured using the accelerometer. The mean and standard deviationof five iterations of each test for the modified and unmodified helmetare provided in Table 2, and depicted in FIG. 12. The data demonstratesthat the composite material produced lower average peak impactacceleration forces than the manufacturer supplied foam, indicating thatthe composite material provided better protection against all impacts.Thus, the composite material provides better protection against injuriesand long-term negative health effects produced by impact accelerationforces than the manufacturer supplied foam.

TABLE 2 Drop G-forces experienced by Riddell Helmet G-Forces Experiencedby Modified Helmet Height Standard N Standard N (in) Mean Deviation(replicates) Mean Deviation (replicates) 6 20.8282 1.754533 5 15.92260.620869 5 12 37.6054 1.609977 5 24.2386 1.228886 5 24 51.155 0.81658655 34.1872 0.4493214 5 36 62.5 1.629793 5 42.0762 1.054014 5 48 79.58982.252049 5 66.8108 0.4535093 5

Example 7 Polydimethylsiloxane/Polyurethane Composite Material

Polyurethane and polydimethylsiloxane (PDMS) composite materials wereproduced with a modulus of elasticity at 100% elongation of 0.105 MPaand 0.032 MPa, to determine the effect of modulus of elasticity on theability of the composite materials to reduce impact acceleration forces.The composite materials included 30% by weight PDMS. The compositematerials were subjected to impact drop tests from a height of 3.5inches with a 25 pound weight. A polyurethane foam that was notimpregnated with a non-Newtonian fluid was also subjected to the impactdrop tests as a control.

The acceleration forces produced by the impact drop tests are shown inFIGS. 14(a)-14(c) for the polyurethane with no non-Newtonian fluid, thecomposite material with a modulus of elasticity of 0.105 MPa, and thecomposite material with a modulus of elasticity of 0.032 MPa,respectively. The data demonstrates that composite material with amodulus of elasticity of 0.032 MPa effectively reduces both the initialimpact acceleration forces and the shockwave acceleration forces incomparison to the polyurethane with no non-Newtonian fluid. By contrastthe composite material with a modulus of elasticity of 0.105 MPaincreased shockwave acceleration forces in comparison to thepolyurethane with no non-Newtonian fluid, and exhibited a minimalreduction of the initial impact acceleration forces. Thus, the compositematerial with a modulus of elasticity at 100% elongation of 0.032 MPaeffectively reduced both the initial acceleration forces and theshockwave acceleration forces, indicating that the modulus of elasticityof the composite materials at least in part determines the impactacceleration performance of the material.

As utilized herein, the terms “approximately,” “about,” “substantially,”“essentially,” and similar terms are intended to have a broad meaning inharmony with the common and accepted usage by those of ordinary skill inthe art to which the subject matter of this disclosure pertains. Itshould be understood by those of skill in the art who review thisdisclosure that these terms are intended to allow a description ofcertain features described and claimed without restricting the scope ofthese features to the precise numerical ranges provided. Accordingly,these terms should be interpreted as indicating that insubstantial orinconsequential modifications or alterations of the subject matterdescribed and claimed are considered to be within the scope of thedisclosure as recited in the appended claims.

It should be noted that the term “exemplary” as used herein to describevarious embodiments is intended to indicate that such embodiments arepossible examples, representations, and/or illustrations of possibleembodiments (and such term is not intended to connote that suchembodiments are necessarily extraordinary or superlative examples).

It is important to note that the exemplary embodiments are illustrativeonly. Although only a few embodiments have been described in detail inthis disclosure, those skilled in the art who review this disclosurewill readily appreciate that many modifications are possible (e.g.,variations in values, manufacturing processes, etc.) without materiallydeparting from the novel teachings and advantages of the subject matterdescribed herein. The order or sequence of any process or method stepsmay be varied or re-sequenced according to alternative embodiments.Other substitutions, modifications, changes and omissions may also bemade in the design, operating conditions and arrangement of the variousexemplary embodiments without departing from the scope of the presentdisclosure.

What is claimed:
 1. A composite material comprising: a polymer foammatrix; and a non-Newtonian fluid impregnated in the polymer foammatrix, wherein the composite material has an elastic modulus of lessthan 0.1 MPa at 100% elongation.
 2. The composite material of claim 1,wherein the polymer foam matrix has a density in the range of about 50g/m³ to about 500,000 g/m³.
 3. The composite material of claim 1 or 2,wherein the polymer foam matrix comprises a material selected from thegroup consisting of elastomers, polystyrene, polyethylene,polypropylene, polyamide, polyurethane, ethylvinyl-acetate, polyethyleneoxide, polyacrylate, cellulose, ethylene vinyl alcohol, polybutylene,polycaprolactone, polycarbonate, polyketone, polyester, polylactic acid,polyvinyl chloride, polyphenylene, and copolymers thereof.
 4. Thecomposite material of any of claims 1-3, wherein the non-Newtonian fluidis not covalently bonded to the polymer foam matrix.
 5. The compositematerial of any of claims 1-4, wherein the non-Newtonian fluid comprisesat least one material selected from the group consisting ofpolydimethylsiloxane, substituted polydimethylsiloxane, 1% w/vpolyethylene glycol in water, 1% w/v polyacrylamide in water, C8-silicaparticles in silicone oil, silica particles in glycerol, and tin oxideparticles in water.
 6. The composite material of any of claims 1-5,wherein the non-Newtonian fluid has a viscosity in the range of about60,000 cSt to about 1,000,000 cSt.
 7. The composite material of any ofclaims 1-6, wherein the non-Newtonian fluid is hydrophobic.
 8. Thecomposite material of any of claims 1-7, wherein the composite materialhas a density in the range of about 50 g/m³ to about 5,000,000 g/m³. 9.The composite material of any of claims 1-8, wherein the non-Newtonianfluid is present in an amount of about 10% to about 90% of the totalweight of the composite material.
 10. The composite material of any ofclaims 1-9, wherein an initial impact acceleration force and a shockwaveacceleration force of an impact cushioned by the composite material areless than an initial impact acceleration force and a shockwaveacceleration force of an equivalent impact cushioned by the polymer foammatrix alone.
 11. The composite material of any of claims 1-10, whereinan impact cushioned by the composite material produces initial impactacceleration force that is at least about 30% lower than an equivalentimpact cushioned by the polymer foam matrix alone.
 12. A method offorming the composite material of any of claims 1-11, comprising: mixinga non-Newtonian fluid and a first polymer foam matrix precursor to forma mixture; adding a second polymer foam matrix precursor to the mixtureof the non-Newtonian fluid and the first polymer foam matrix precursor;mixing the mixture of the non-Newtonian fluid, first polymer foam matrixprecursor, and second polymer foam matrix precursor to form a mixture;wherein mixing the mixture of the non-Newtonian fluid, first polymerfoam matrix precursor, and second polymer foam matrix precursor resultsin the foaming of the mixture and the formation of a polymer foam matrixmaterial, and curing the mixture of the non-Newtonian fluid, firstpolymer foam matrix precursor, and second polymer foam matrix precursorto form the composite material; and wherein the composite material hasan elastic modulus of less than 0.1 MPa at 100% elongation.
 13. Themethod of claim 16, further comprising disposing the mixture of thenon-Newtonian fluid, first polymer foam matrix precursor, and secondfoam polymer matrix precursor in a mold prior to curing the mixture. 14.A product for reducing acceleration forces in an impact, comprising thecomposite material of any of claims 1-11.
 15. The product of claim 14,wherein the product is selected from the group consisting of a helmet,clothing, a uniform, footwear, a glove, a case for an electronic device,a housing for an electronic device, a vehicle seat, a vehicle headrest,a vehicle dashboard, a vehicle door component, playground equipment, anexercise mat, a gym mat, and a packaging material.